About 40% of all ULIGs have Liner type optical spectra
([482];
Veilleux et
al. 1999). Spectropolarimetric, near-infrared spectroscopic and MIR
spectroscopic observations have been carried out in a number of such objects;
none of them shows any obvious sign of an obscured BLR, suggesting that
they are powered by starbursts
([440];
[418];
[269];
[412]).

We have plotted on the diagnostic diagrams
5007 /
Hvs6583 /
H and
6300 /
H all luminous and
ultraluminous IR galaxies for which the
required line ratios have been published
([482];
Veilleux et al. 1999),
excluding the Seyfert 1s for which the relative fluxes of the narrow component
of the Balmer lines are generally not available. These plots are shown
in fig. 4. The two objects with the strongest
[O I] lines are PKS2338+03,
a radio galaxy and NGC6240, a well known AGN
([451]).
Comparison with
fig. 3 shows that in addition to
low excitation H II regions and
Seyfert 2s, there is a cluster of objects around
5007 /
H ~ 1.6,
6583 /
H ~ 0.8 and
6300 /
H ~ 0.1; these
are the objects which have been classified as Liners; however they seem to be
different from the Liners in fig. 3
which are mostly associated
with AGNs, suggesting that, indeed, they are not genuine AGNs.

Figure 4. Diagnostic diagrams for luminous
and ultraluminous
IR galaxies, excluding Seyfert 1s. The regions containing H II regions,
Seyfert 2s, and classical Liners have been delineated as in
fig. 3. H II
regions
are shown as crosses, Seyfert 2 as open circles. The black squares are the
objects called ``Liners'' in the original papers (see text); they
cluster in a region which is well outside the region occupied by the
``classical'' Liners, i.e. Liners associated with an AGN.